In Human stages of life, the first five years of life, which consists mainly of children, are the most fundamental to human physical and intellectual development and can determine their potential to gain knowledge and thrive for a lifetime. It is vital to reveal that: for young children, every single moment of life counts. Mortality of the child is being influenced by underlying factors, both biological and socio-economic. In recent years, early mortality (i.e. mortality before the age of five) in developing countries has been receiving considerable research attention from scholars interested in population-development interactions. With these, it is therefore of paramount essence to identify the factors most prominent in the determining of the childhood mortality, so as to be able to combat them. In this book, the knowledge and understanding of the silent child killer; the under-five mortality, is revealed with focus on the south west region of Nigeria.